Power-driven dermatome



2 Sheets-Sheet l G. J. HOOD POWER-DRIVEN DERMATOME M M v m m u 4 Liz-Zara e i a ht: m E w i 6 ml? W 0 mm. m {mm .4 M I W! m lhl 7 -Q W Oct. 12, 1954 Filed Sept. 22, 1952 Oct. 12, 1954 G. J. HOOD 2,691,377

POWER-DRIVEN DERMATOME Filed Sept. 22, 1952 2 Sheets-Sheet 2 Patented Oct. 12, 1954 UNITED STATES PATENT OFFICE POWER-DRIVEN DERMATOME George J. Head, Lawrence, Kans. Application September 22, 1952, Serial N 0. 310,796

1 22 Claims. 1

This invention relates to surgical'instruments, and more artic'ularly to a cutting device in the nature of a dermatome for removing skin from a patients body to be used subsequently in grafting operations, an object being to provide a power operated instrument of the type having a reciprocable blade so arranged with other cooperating elements of the "device to provide accuracy in the cutting operation and render the cutter easily operable by a single user without necessitating additional aid.

It is the primary object of this invention to provide a derm'atome having the proper relationship between the leading edge of the gage bar and the cutting edge of the knife blade "so that the graft cut will be of accurate thickness and the knife will cut at all times without gouging though the instrument is tilted relative "to the skin.

It is the most important object of this invention to provide a dermatome that includes a reciprocable knife having an elongated cutting edge, .disposed immediately below -a gage 'bar'that is adjustable toward and away from the cutting edge to determine the thickness "of the cut, the gage 'bar being precisely disposed so as to permit accurate adjustments and at the same time not interfere with the cutting action.

Another very important object hereof is to providein an instrument of the aforementioned class, a combination gage bar and knife blade assembly wherein the gage bar is so disposed as to assure accurate thicknesses in the cuts being made, notwithstanding variances in the angularity of the'instrument to the "body of the patient during use of the instrum'entto'ma'ke the cut.

Another important object of this invention is to provide a dermatome adapted for cutting strips of indeterminate length and selected widths, as well "as thicknesses precisely. as desired .by the user, there being means for providing simple adjustments without the necessity of using complicated tools or the skill of an engineer.

.It is an aim of this invention to provide means for adjusting the aforesaid gage :b'ar through novel application of dual eccentric elements, one of which is normally set at the factory 'by the manufacturer, and the other being employed by the user for making more precise adjustments immediately prior to placing the instru ment in use.

A still further aim of'this invention is to provide one or more removable plates/adapted for support by the gage bar and having parts :dis posed directly infront of the cutting edge of the .knife blade to determine the width of :cut.

It is an additional aim hereof to include in an instrument of the type forming the subject matter of this invention, guard means adjacent each rendrespectively of the knife blade to obviate gouging into the patient during the cutting operations at the ends of the cutting edge.

Another object :of this invention is to provide a dermatome having a quickly and easily removable knife blade that is held in place against the lowermost face of a knife bed through employment of a resilient clamp, the clamp :being readily removable and :there being provided a novel guide member having the function of releasably receiving the clamp, as well as the knife blade itself.

A further obiect of this invention is to provide noveldriving mechanism for the reciprocable cutter blade that includes as a part thereof, a quickly releasable mounting assembly for the blade itself.

A still further obiec't hereof is the provision of a reciprocable yoke adapted for operable connection with the rotatable drive shaft of :an electric motor "or other prime mover, "the yoke itself being swingable on its reciprocalble axis and having a trigger arm swingably mounted thereon for receiving the knife blade, whereby swinging action of the yoke and the trigger arm determines the manner of removal and replacement :of the knife :blade.

As will hereinafter appear, the present invention has a large :number of additional, more minor (objects, :all :of which will be made clear or become apparent as the following specification iprogresses.

In "the drawings:

Figure 1 is a top plan view of .a power driven de-rmatome made pursuant to my present invention.

Fig. 2 is .-a front elevational view thereof.

Fig. ,3 is an end elevational view thereof.

Fig. 4 is an enlarged, transverse, cross-sectional view taken on irregular line IV-lV of Fig. l with the width plate removed.

Fig. 5 is a reduced, fragmentary, cross-sectional'view taken on line "VV of Fig. '4,1o'oking "in the direction of the arrows.

Fig. 6 is an enlarged, fragmentary, detailed, cross-sectional view taken on line VI VI of Fig. 5.

Fig. 7 is a reduced, fragmentary view of the lowermost face .of the rderma-tome, parts being broken away to reveal details of (construction.

Fig. .8 is .a schematic, -cross-sectional viewillustrating a gage bar and an incorrectly positioned cutter blade, all of which becomes inop- 3 erable during tipping relative to the skin, so as to present a better understanding of the invention.

Fig. 9 is a view similar to Fig. 8 showing the operation of the present invention; and

Fig. 10 is a fragmentary, cross-sectional view similar to Fig. 4 showing the width plate in place.

Many types of dermatomes and other cuttin instruments involving the use of an elongated, reciprocable knife blade have heretofore been developed, but so far as I am aware, none have satisfactorily eliminated all interference with the desired action of the blade in cutting relatively thin strips from an object such as the body of a patient that is extremely pliable and which tends to yield under the impact of cutting instruments of this type. Manifestly, it is essential that the instrument be provided with means for determining the thickness of cut and the means heretofore provided usually includes a gage bar or guard that is disposed forwardly and/ or in front of the cutting edge of the blade itself, thereby interfering with its desired operations. These defects have been eliminated in the instrument about to be described through the provision of a novel gage bar and knife blade assembly.

The instrument includes a frame broadly designated by the numeral [0. Frame i6 includes a pair of spaced, parallel side walls I2 and 14 that are interconnected adjacent the lowermost edges thereof by a knife bed 16, by a rear wall l8, and by a partition 20, rear wall 18 and partition 26 being relatively parallel, perpendicular to the side walls l2 and I4 and also joined to the knife bed [6 on the uppermost face of the latter. A cover plate 22 between the side walls (2 and I4, and between the rear wall [8 and partition 26, closes a hollow compartment 24. Cover plate 22 is removable and to this end, there is provided a number of tubes 26 rigid to the lowermost or innermost face of the plate 22 between the wall I6 and partition for receiving bolts 28 that interconnect the partition 20 and the rear wall l8.

Fhe knife bed I6 is cut away to present an elongated, forwardmost, longitudinal edge 30, provided with a rearwardly beveled portion 32. An elongated, flat knife blade 34 is mounted on the lowermost face of the bed I6 for reciprocation on its longitudinal axis along a path of travel parallel with the forwardmost edge 30 of bed l6. Blade 34 extends forwardly beyond the edge 36 and terminates in a cutting edge 36 that is spaced rearwardly from the forwardmost extremities of the frame l6.

The depth of cut, by the edge 36 of blade 34, is determined by an elongated or rectangular gage bar 38 that is disposed directly above the cutting edge 36 and between the walls 12 and M of frame In. It is highly important that the edge 36 of blade 34 be parallel with the lower edge 4| of gage bar 38 and in alignment with a central longitudinal plane through the gage bar, said plane being perpendicular to the upper face of blade 34.

The precise disposition of the gage bar 38 becomes further apparent when it is noted that a pair of guards 44, rigid to the knife bed [6, are

disposed directly in front of the cutting edge 36 at each of the two ends thereof. The guards 44 are effective in preventing gouging of the patient during the cutting operations by preventing the ids of the cutting edge 36 from reaching the patients body during the cutting of skin therefrom.

The gage bar 38 is rigidly secured to a pair of spaced arms 46 that depend from a shaft 48 that interconnects the walls l2 and i4 of frame l0. Shaft 48 is rigidly and eccentrically mounted in a pair of cams 50 and is also eccentrically mounted in bearing elements 52. There is a bearing element 52 rotatably mounted in each wall 12 and I4, the latter carrying setscrews 54 that bear against the rotatable elements 52 to hold the same against rotation. Thus, each element 52 constitutes a bearing for rotatably receiving shaft 48.

Hub 55, fixed to shaft 43 carries a resilient pointer 56 that bears against the outermost face of the wall 12 and indicates the depth of cut by virtue of calibrations 58 on said outermost face of wall I2. It is seen that rotation of the bearing elements 52 within the walls [2 and I4, raises and lowers the members 50, shaft 48, arms and gage bar 38 toward and away from the uppermost face of blade 34 or the cutting edge 35 thereof. Adjustments of elements 52 are made at the factory and the setscrews 54 are brought to bear against the bearing elements 52 to normally hold the same against rotation. Thereupon the operator may make more precise adjustments with respect to the distance between the lowermost edge of the gage bar 33 and the cutting edge 36 by manipulation of the pointer 56. Such action rotates the shaft 48 and accordingly, the members that are rotatable within their arms 46 to raise and lower the gage bar 38. Grooves 60 in the knife bed 16 receive the ends of the gage bar 38 and guide the same along its reciprocable path of travel toward and away from the knife blade 34.

The lowermost longitudinal edge of the gage bar 38 is preferably formed as shown in Figs. 4, 9 and 10 of the drawings, and edge 36 should be disposed relatively close to legs 46 of a U-shaped plate 42 when the latter is mounted on the gage bar 38 (see particularly Fig. 10) It is noted that the legs 40 are disposed forwardly of and in overlapping relationship to portions of the cutting edge 36 as distinguished from the gage bar 38 that is entirely above the knife blade 34 where the same will not interfere in any way whatsoever with the cutting action of the instrument when the same is placed in use. The legs 46 of the plate 42, when the latter is placed in use, being in front of the edge 36, limit the extent of cutting action and therefore, determine the width of the strip to be cut.

The width determining plate 42 is used only when the strip to be cut is of less width than the distance between the proximal innermost ends of the guards 44. It is contemplated that a plurality of plates 42 shall be provided for use with the instrument as desired, and since the same are identical except only for the differences in distances between the legs 48, only one plate 42 has been illustrated in the drawings. Plate 42 which lies directly against the outermost face of the gage bar 38 is provided with releasable fastening means 62 to hold the same against displacement.

Any suitable prime mover may be utilized for driving the blade 34 and the same may either be removably attached directly to the dermatome or connected thereto through the medium of a flexible shaft. For purposes of illustration, there is shown fragmentarily in Fig. 4 of the drawings, a casing 10 of an electric motor havmg a'fd'rive shaft I2 within a tubular housing 14. Shaft '12 is removably connected with a driven crank shaft 16 forming apart of the dermat'ome hereof and mounted within a tubular housing 78 that releasably receives the housing 1'4 jof the motor.

One way of interconnectingfthefhousings "I4 and!!! isillustrated and includes a spring-loaded plunger 86 on the housing 76 that extends into a'hole '62 within an annular groove 63 formed in the tube M. The tubular housing I8 is carried by the rear wall It of frame I and communicates with the compartment 24. The crank shaft 16 is rotatably mounted in a bearing, bushing or the like, carried by the housing I8 as shown in Fig. '4, and has a disc 64 rigid to the innermost end thereof and disposed within the compartment '24. An inwardly extending pin 66 on the disc "84 is eccentric'to the axis of rotation of "shafts Y2 and 16 and extends through a polygon'a'l-bloc'k 66 carried by a yoke-like drive member within the compartment 24 and broadly designated by the numeral 96. v

Yoke 96 consists of a pair of spaced, elongated -bar s 92 (Fig. '5) which slidably receive the block 68 for reciprocation between the bars 92 toward and away from a shaft 96 that interconnects the 'walls 12 and 14 within compartment 26 below block 88 and above the bed I6. The bars 92 of yoke 96 are mounted on the shaft 94 intermediate the ends of the bars 62 for reciprocation "of the yoke 96 along the shaft 94 and for swinging movement on shaft'64 in the manner illustrated by dotted lines in Fig. 4.

A substantially L-shaped trigger arm 96 is carried by the yoke 96 at the lowermost end thereof below the shaft 94 and between the bars 92. A pin 98 parallel with the shaft 94,'pivotal1y mounts the trigger arm 96 and is carried by the "bars 92. Pin 96 extends beyond one of the bars 92 as shown in Fig. '5, and has an elongated leaf spring lllfl secured thereto. Spring I 66 extends 'u'p'wardly between the shaft 9 3 and the rear wall "I 8,and'norma-lly bears against the innermost face "of the latter as is clear in Fig. 4.

The bed I6 has an opening I 62 for clearing the trigger arm 96 that extends forwardly beneath the knife bed I 6 into a cavity I66 formed in the lowermost face of the latter. Trigger arm 96 overlies the blade 34 and has a trigger pin I66 depending therefrom that extends into an open- 'ing provided therefor in the blade 34 midway between the intermediate ends thereof.

A manually operable push button I 68 carried by *the rear wall I 6 below the housing I6, is aligned with the drive member or yoke 96 for imparting swinging movement thereto and to the trigger arm 96 when blade 34 is removed or replaced.

An elongated guide member [I6 is mounted ireotly on the lowermost face of the bed I 6 and is provided with a cavity H2 for clearing the trigger pin I66 when assembling the parts of the dermatome. A guide channel I I4 along one lon- "g'itudinal edge of the member I I6, slidably receives the rearmost longitudinal edge of the blade '34 and a second channel III; along the opfp'osite longitudinal edge of the member H6, rec'eives leg H8 of a resilient clamp I26. Leg II8 bears against the lowermost face of the bed II6 rearwardly of the guide member H6, and is held within the guide channel I I6 by a plurality of studs I22 depending from the bed I6. A small :dimple ion the leg I I8 bears against the proximal endof the guide member H6 as shown in blade 34. By virtue of the resilient nature of the clamp I26, the edge I26 is held biased against the blade 32;, thereby cooperating with theguide I It in holding the blade 34' against the lowermost face of bed I 6. I

While the operation of the dermatome hereof becomes apparent from the foregoing description, it is well to point out that reciprocable movement of the blade #34, through rotation of the shaft I2, takes place by virtue of the-oscillation of the yoke 96 on the shaft 66. As disc 86 rotates, the block 68 reciprocates toward and away from the shaft 94 by virtue of the rotat-ive mounting of block 68 on the eccentric pin 66.

Accordingly, the blade 36 is reciprocated through the trigger arm 66 along a path of travel parallel with the shaft 9 1. During normal operation, the yoke 96 is disposed as illustrated byfull lines in Fig. 4, and is held against swinging movement toward the partition 26- by spring I66. This spring V66 serves to hold the trigger arm 96 interlocked with the blade 3'4, keeping the latter within the guide channel H4.

When it is desired to remove the blade 34, the clamp I26 is shifted in either direction'longitudinally thereof to remove the same entirely from the guide member H6. Thereupon, the operator pushes inwardly upon the button I66 against the action of spring I66, to cause relative swinging movement between the yoke 66 and the trigger arm 9'6. Such action shifts the blade 66 away from the bed I6 and blade 34 will thereupon readily drop from within the channel IM and from the projection I06.

Replacement of the knife 64 is effected while the push button I66 is depressed. The functions of the clamp I 26, the gage bar 66, the plate 52 and the guards '44, as well as the operation of gage bar 68, through manipulation of pointer 66 and/or the bearing elements 62 upon loosening of the setscrews '54, have all been made clear 'as the foregoing description progressed, and

need "not be repeated. v

During use, the housing 16 or the prime mover I6 itself, is utilized as a handle and the instrument is moved across the patients'body along the area from which skin is to be removed and such strip of skin 63 moves between "the lowermost face 61 of gage bar '96 and the cutting edge -36 of knife 34, upwardly along the inclined portion 62 of bed I6, and thence into the space provided between the gage bar 98 and the partition 26, as well as between the side walls It and It. Skin 4 6 automatically folds upon itself upon the bed I6 in front of the partition 26 and therefore, a single operator may use the dermatome without need of assistance in handling the removed skin strips 43 during the cutting operations. The guards 44 and/or the inclined portion of clamp I26 immediately behind the edge I26 thereof, ride along the surface being out, depending upon the angularity at which the instrument is held by the'user. It is to be. stressed however, thatsuch angularity has no effect upon the cutting action and particularly upon the thickness of the skin being cut because of the novel arrangement of the gage bar 38 with respect to the knife 34 immediately therebelow.

The gage bars 38-38 and blades 34'-34 are shown in Figs. 8 and 9 as they will appear in relation to the surface of the body of the patient when the dermatome is tilted as it often will be when in use. When cutting a graft 43, it often is difficult or impossible to keep the blade 34 approximately fiat against the body of the patient.

In order to fully explain the interaction between the skin, the gage bar and the knife blade when the dermatome is tilted so that the blade face is lifted out of parallelism with the skin surface, Fig. 8 purposely shows the blade edge 36 set too far back to cut a graft. When using the dermatome, the gage bar 38' presses against the body of the patient and moves in the direction of the arrow which is parallel to the body of the patient. The skin, indicated by a broken line, flows along the forward face and around the leading rounded edge 39' of the gage bar 38 as the dermatome is pushed forward. The pressure of the gage bar 38 against the body of the patient forces the flesh into compression in the general area C ahead of the gage bar :38', while the skin surface behind the gage bar 38' is pulled in tension along T. This tension soon pulls the skin out of contact with the lower face M of the gage bar 38' along an edge located approximately at d. The knife edge 36' is set too far back in Fig. 8 to cut the skin.

To cut a graft 43 when the dermatome is tilted, it thus is essential that the cutting edge 36 of the knife 34 must be forward of the edge :1 where the skin withdraws from its contact with the gage bar 38 (Fig. 9).

Also, it is necessary to maintain some pressure, and hence friction, between the skin and the gage bar 38 near the line where the graft 43 is cut so as to keep the skin from vibrating with the reciprocating blade 34, since such vibration tends to make the blade 34 shred the cut graft 43. As the flowing skin approaches the edge d in Fig. 9, the pressure decreases and the friction becomes zero.

In addition, the lower face of the knife blade 34 also tends to lift the skin away from its contact with the gage bar 38. The three conditions just stated closely limit the location of the knife blade 34 in its relation to the gage bar 38 in order to meet the requirement that the dermatome is to cut a uniform graft 43 when the dermatome is applied at varying angles to the surface of the skin.

The related gage bar 38 and knife blade 34 as shown in Fig. 8, will cut a graft only if certain limited conditions are met: The blade 34' must be held flat, or nearly flat, against the skin. Even then there will be a tendency to shred the graft, and a uniform graft cannot be assured unless additional means are provided to keep the skin from vibrating in the direction of the reciprocating knife edge 38'. Also, to be sure of cutting a uniform graft, it usually is necessary to force the skin against and around the lower face 4| of the gage bar 38' by pulling on the edge of the cut graft. And, the graft will be severed from the patient should the dermatome be tilted forward through a rather small angle.

The area of contact between the skin and the lower edge of the gage bar can readily be demonstrated by coating the skin with some pigment such as printer's ink, and then pressing the gage bar against the skin and moving it across the coated part of the skin, while holding the gage bar tipped forward at a slight angle as indicated in Fig. 8. The markings left by the pigment on the lower edge of the gage bar will show that the skin follows the gage bar but a short distance around its lower edge, whether the edge of the gage bar is flat or rounded. And the imprint of the skin on the gage bar becomes fuzzy near the edge where the skin leaves the gage bar, thus indicating that the contact is not firm, and that conditions for cutting a graft are not stable.

Fig. 9 shows the correct location of the knife edge 36 to the gage bar 38 of the dermatome in order to satisfy the three above-explained requirements that must be met if the dermatome is to cut uniform grafts 43 when the dermatome is held at various angles in relation to the body of the patient so as to give the operating surgeon considerable freedom in holding the dermatome when cutting a graft 43, to permit cutting a graft 43 from the less accessible areas of the body, and to avoid the need for having an assistant to stretch the graft 43 by pulling thereon while it is being out. A dermatome designed to conform with Fig. 9 will cut uniform grafts 43 as it is tilted at increasing angles up to 45 degrees or more.

In Fig. 9, the dermatome is being moved parallel to the body of the patient in the general direction indicated by the arrow. The skin surface of the patient and the cut graft 43 are indicated by broken lines. The knife blade 34 is inclined at an angle with the surface of the skin, and the gage bar 38 is tilted forward at a corresponding angle. The distance of the knife edge 36 from the lower face 4| of the gage bar 38 is closely equal to the thickness t of the graft 43 that is being cut. The knife edge 36 is placed forward of the edge at where the skin begins to be pulled away from contact with the lower face 4! of the gage bar 38. The knife edge 36 must also be rearward of the leading edge 39 of the gage bar 38 before the distance of the knife edge 36 from the lower face of the gage bar 38 is appreciably increased by the rounding of the leading edge 39 of the gage bar 38. The edge of the knife blade 34 must be precisely located in order to meet the three limiting conditions explained in previous paragraphs, even when the dermatome is tilted as much as degrees, since the location of the edge 11 changes with the angle of tilt. In the dermatome, the knife edge 36 must be placed directly opposite a narrowly limited area of the lower edge 4| of the gage bar 38. The width of this area is determined as described above. This width is estimated as being less than three times the thickness of the average graft 43 that is cut by the dermatome. If the knife edge 36 is placed in front of the leading edge 39 of the gage bar 38, then the patient may be gouged, the thickness of the graft will vary with the pressure and the angle of tilting of the dermatome, and the graft 43 is likely to be shredded.

When the graft 43 is cut to the desired length, it is severed from the body of the patient by lifting the dermatome with the motor 10 running.

Since, as above indicated, it is primarily the aim hereof to improve upon the prior art with respect to gage bar-knife blade relationship, attention is called to Brown et al., No. 2,457,772, the references therein cited, and Eidam, No. 2,428,018.

All of the aforementioned features of the instrument hereof are highly important to efficient operation and each performs its part in presenting a delicate instrumentality requiring high precision in the particular use to which the same is to be placed.

Having thus described the invention what is claimed as new and desired to be secured by Letters Patent is:

1. In a dermatome, a frame having an elongated knife bed; an elongated, reciprocable knife lade on one face of the knife bed and having a longitudinal cutting edge extending forwardly beyond the normally forwardmost, longitudinal edge of the bed; and an elongated gage bar on the frame, said gage bar extending along said bed edge in overlapping relationship to the latter, said cutting edge being parallel with the bar in alignment with a central longitudinal plane passing through the gage bar and disposed perpendicularly to the upper face of the bed.

2. In a dermatome, a frame; an elongated knife blade mounted on the frame for reciprocation on its longitudinal axis and having a longitudinal cutting edge; an elongated gage bar carried by the frame, said gage bar having a longitudinal face spaced from said cutting edge of the blade; and a plate on the gage bar, said plate having a portion overlapping a portion of said cutting edge of the knife blade.

3. In a dermatome, a frame having an elongated knife bed; an elongated, reciprocable knife blade on one face of the knife bed and having a longitudinal cutting edge extending forwardly beyond the normally forwardmost, longitudinal edge of the bed; an elongated gage bar extending along said bed edge in overlapping relationship to the latter and overlying said cutting edge; and mounting means for securing the gage bar to the frame and normally holding the same against movement relative to the frame.

4. In a dermatome, a frame having an elongated knife bed; an elongated, reciprocable knife blade on one face of the knife bed and having a longitudinal cutting edge extending forwardly beyond the normally forwardmost, longitudinal edge of the bed; an elongated gage bar extending along said bed edge in overlapping relationship to the latter and overlying said cutting edge; and structure mounting the gage bar on the frame for movement toward and-away from said knife blade and provided with means for holding the gage bar in predetermined positions relative to the frame.

5. In a dermatome as set forthin claim 4 wherein said structure includes a rotatable element having cam means operably coupled with the gage bar to move the latter upon rotation of said element.

6. In a dermatome as set forth in claim 5 wherein said structure is provided with bearing members for said element carried by the frame for movement relative thereto for shifting the latter and the gage bar toward and away from the knife blade.

7. In a dermatome, a frame having an elongated knife bed; an elongated, reciprocable knife blade slidable on one face of the knife bed and having a longitudinal cutting edge extending forwardly beyond the normally forwardmost, longitudinal edge of the bed; and a resilient clamp on said bed and bearing against the blade for holding the latter against said face of the bed.

8. In a dermatome, a frame having an elongated knife bed; an elongated, reciprocable knife blade slidable on one face of the knife bed and having a rearmost edge and a longitudinal cutting edge extending forwardly beyond the normally forwardmost, longitudinal edge of the bed; a guide on said face of the bed slidably receiving said rearmost edge of the blade; and a resilient clamp carried by the bed and the guide and bearing against the blade for holding the latter against said face of the bed.

9. In a dermatome as set forth in claim 8 wherein said guide consists of an elongated bar having opposed channels, one slidably receiving the blade, the other slidably receiving said clamp.

10. In a dermatome, a frame; an elongated knife blade mounted on the frame for reciprocation on its longitudinal axis and having a longitudinal cutting edge; an elongated shaft carried by the frame; a drive member mounted on the shaft for reciprocation therealong; and a trigger arm attached to the drive member and connected with said blade, said drive member and said trigger arm being swingable relatively in one direction to a position releasing the blade from the trigger arm.

11. In a dermatome, a frame; an elongated knife blade mounted on the frame for reciprocation on its longitudinal axis and having a longitudinal cutting edge; an elongated shaft carried by the frame; a drive member mounted on the shaft for reciprocation therealong; a trigger arm swingably mounted on the drive member and connected with said blade; and releasable means connected with said arm for yieldably holding the same biased against the blade, said drive member being swingable on the shaft in one direction to a position releasing the blade from the trigger arm.

12. In a dermatome as set forth in claim 11 wherein is provided a drive shaft, and a coupling member operably interconnecting the drive shaft and the drive member for reciprocating the latter, said drive member and said coupling member being relatively slidable.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,594,613 Hagen Aug. 3, 1926 2,288,709 Hood July 7, 1942 2,579,029 Barker et a1 Dec. 18, 1951 

